The present invention relates generally to radioactive decontamination devices and more particularly to a machine for removing radioactive contamination from the wall of an access hole of a radioactive hot cell.
Hot cells are shielded chambers containing radioactive material. The shielding is usually in the form of several feet of concrete for the walls, floor, and ceiling, with several feet of special glass for the viewing windows. Each hot cell generally has one or more access holes or ports in the thick concrete walls. Of varying size, such as 10 inches in diameter, they are generally of a right circular cylindrical shape aligned horizontally to the floor of the hot cell. The access holes serve as passageways to put radioactive material and tools into the hot cell and to remove them from the hot cell. Access holes are also used for manipulators installed in the radiation shielding wall. Radioactive contamination may occur on the walls of an access hole, such as during the removal of a manipulator for maintenance. Quite often the boot covering the inner section of the manipulator is damaged, burned, or badly contaminated. When the unit is withdrawn, particles fall off in the hole. The hole is sometimes as much as three and one half or four feet long. These radioactive particles may also be thermally hot and may damage the new boot if not removed. They will also contaminate the operating gallery side of the shielding wall if allowed to escape after a manipulator is removed.
Prior to this invention, radioactive contamination was removed from the walls of access holes of hot cells by individuals using manual cleaning techniques. A lead shield would be installed in the hole and individuals would hand clean behind it, manually scrubbing the hole, with simple tools such as mops, swabs, and scrapers. These individuals would receive considerable radiation exposure in the hole and during handling of the swabs and shield.